This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There are currently no effective vaccines to prevent RSV in children, and treatment options for RSV infected individuals are extremely limited. Ribavirin is currently the only licensed therapeutic agent for RSV lower tract disease in hospitalized infants. Although initial clinical trials of ribavirin suggested improved clinical outcome in hospitalized children with severe RSV disease, recent studies in children with or without underlying conditions failed to demonstrate efficacy. It is evident that improved modes of therapy are needed to treat children with serious RSV infections. One such possibility is the use of antibodies directed against neutralization epitopes of RSV. There have been 3 previous small treatment studies with RSV-IGIV (Respigam[unreadable];study RSV9201), palivizumab (Synagis[unreadable];study MI-CP009), and motavizumab (MEDI-524;study MI-CP106). In these trials, passive therapy with RSV-specific antibody was shown to be safe and well tolerated with no evidence of acute disease enhancement or long-term sequelae. All 3 studies demonstrated a reduction in RSV viral load in the lower respiratory tract. The study with motavizumab showed a significant reduction in the cultivatable virus in the upper airway compared to placebo, and there was a trend toward a dose-effect with greater reduction in viral load as measured by real-time RT-PCR in the 30 mg/kg motavizumab-treated children. However, some of the children treated with the 30 mg/kg dose of motavizumab did not have consistently detectable motavizumab levels in the nose. With the encouraging findings of reduction in viral load and a suggestion of clinical benefit in the previous small studies, the current study is being conducted to determine if there can be a further reduction in viral load and if higher levels of motavizumab can be attained in the upper respiratory tract in children hospitalized with RSV when treated with a higher dose of motavizumab. If the findings from this initial study are positive, then additional studies of the effect of motavizumab on clinical outcomes in hospitalized children treated for RSV would be warranted.